This application is based upon and claims the benefit of Japanese Patent Applications No. 11-121166 filed on Apr. 28, 1999, and No. 2000-42896 filed on Feb. 21, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates generally to photo sensors, and particularly to vehicle photo sensors, which are suitable for an auto-light sensor for automatically turning on or off a headlight, a sunlight sensor for detecting a quantity of solar radiation to control a vehicle air conditioner, and the like.
2. Description of the Related Art
In recent years, a vehicle photo sensor is required to include a sensing element (photodiode) and a signal processing circuit, which are integrated in one chip, to achieve size reduction, functional improvement, and low cost thereof. This kind of photo sensor is disclosed in JP-A-10-173158. The photo sensor has a shielding film for covering a transistor, and determines a distance between a shielding film edge portion and a transistor edge portion to securely prevent faulty operation of the transistor caused by strong light (sunlight).
In the photo sensor, however, the shielding film must be formed at a wide region to prevent the faulty operation of the transistor, resulting in large chip size. When the photo sensor is used as an auto-light sensor, the photo sensor is required to have sufficient sensitivity to detect very weak sunlight in the evening with low illuminance, especially immediately before sunset. Because of this, an area of a photodiode for sensing sunlight needs to be increased so that a detection signal is increased. This results in further increased chip size. In the conventional sensor, because the photodiode is formed in the same substrate as that for circuit elements for constituting the signal processing circuit, the substrate cost and processing cost are high. Further, because the photodiode is disposed at the central portion of the substrate, the layout of the circuit elements is limited by the photodiode.
The present invention has been made in view of the above problems. An object of the present invention is to provide a photo sensor with a reduced size at low cost, while preventing faulty operation of a circuit thereof.
According to the present invention, a photo sensor has a first semiconductor chip and a second semiconductor chip mounted on the first semiconductor chip. A photoelectric transformation element for transforming a quantity of light incident thereon into a signal is provided in a surface portion of the second semiconductor chip, and a circuit element for manipulating the signal is provided in a surface portion of the first semiconductor chip under the second semiconductor chip. Further, a shielding film is disposed between the first and second semiconductor chips.
The shielding film prevents light from entering the circuit element to prevent faulty operation of the circuit element. Further, because the photoelectric transformation element and the circuit element are provided in the separate semiconductor chips, each size of the chips and the area of the shielding film are decreased and the manufacturing cost is reduced. The layout of the circuit element is not limited by the photoelectric transformation element.